With the soaring cost of energy, it is essential to develop new light-weight materials that can provide better thermal insulation performance in housing and construction industries and high structural strength for automotive, aerospace, and electronic applications.
For example, in the housing industry, doubling the ‘R’ value of current thermal insulation materials can save $200 million annually in heating/cooling costs for families in the U.S. In today's average vehicles, as much as 5-10% in fuel savings can be achieved through a 10% weight reduction. Polymeric foams have been used in many applications because of their excellent strength-to-weight ratio, good thermal insulation and acoustic properties, materials savings, and other factors. By replacing solid plastic with cells, polymeric foams use fewer raw materials and thus reduce the cost and weight for a given volume. The North American market for foamed plastic insulations exceeds $3 billion annually, while global demand is above $13 billion. However, polymer foams, except sandwich composite foams, are rarely used as structural components in the automotive, aerospace, and construction industries because of poor mechanical strength and low dimensional and thermal stability, when compared to bulk polymers.
In recent years, several researchers have reported that foams can possess excellent mechanical strength if the cell size is smaller than the typical flaw size in bulk polymers, i.e., <10 μm. Microcellular foams can reduce material usage and improve mechanical properties simultaneously. They have been commercialized for some applications (i.e., MuCell by Trexel). However, they require specially designed processing equipment, have a narrow process window, and are still not strong enough for structural applications.
Closed-cell plastic foams have better thermal insulation efficiency than glass fiber or plywood insulation materials, but the application of plastic foams in the housing industry is limited due to their poor fire resistance. A drastic reduction of thermal conductivity has been observed when the cell size is reduced to the nanoscale, e.g., aerogel. These nanofoams are currently made of ceramics in thin films and are very expensive. Foams with ultra-low density also provide better thermal insulation. To increase the expansion ratio during foaming in order to achieve ultra-low density, an expensive vacuum system is often needed in the industrial foam extrusion line.
Another critical issue faced by the foam industry is the blowing agent. Traditional chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) blowing agents cause ozone depletion and will be banned by 2010 according to the Montreal Protocol. Carbon dioxide (CO2) is an attractive replacement for the ozone-depleting blowing agents because it is low-cost, non-toxic, nonflammable, and not regulated by the Environmental Protection Agency (EPA). Since insulation foams used in houses dramatically reduce energy consumption and thus decrease the pollution generated by power plants, the use of CO2 has both a direct and an indirect benefit to the environment. However, CO2 has a lower solubility in most polymers than traditional blowing agents. It also has a higher diffusivity leading to a quick escape from the foam after processing. While this ensures fast mixing, it also offers a quick escape from the foam after processing resulting in a lower expansion ratio (i.e., higher foam density). The presence of CO2 complicates the manufacturing process and thus results in a high processing cost.
An exemplary embodiment of the present invention seeks to dramatically improve the insulation performance of polymer foams using zero-ozone depleting blowing agents such as, but not limited to, CO2 and/or water. In addition to enhancing the insulation value, which may lower the energy cost of the building, exemplary embodiments of the present invention include developing and manufacturing new truly green polymer insulation foam products.
An exemplary embodiment of the present invention may use at least one blowing agent that has minimal impact on the environment (e.g., zero-ozone depleting blowing agents such as CO2 and/or water). One exemplary embodiment of the present invention relates to polystyrene and/or thermoplastic polymer or polymer blend composite foam or a foamable polymeric material precursor, which contains foaming facilitating material and/or at least one of 1-dimensional, 2-dimensional, and 3-dimensional nano/micro-materials in a polystyrene and/or thermoplastic polymer and/or polymer blend matrix to carry a co-blowing agent such as water without using any surfactant-like molecules and/or polymers, having or adapted to have the properties of low density, high-R value, good mechanical properties, and fire retardance thereof. Exemplary embodiments of the present invention include various manufacturing methods, which are not limited to extrusion, batch molding, and injection molding. One example includes synthesis and CO2 and water-based extruded foaming of such a material. Exemplary embodiments of the present invention also include products made from the materials and/or methods discussed herein.
In addition to the novel features and advantages mentioned above, other benefits will be readily apparent from the following descriptions of the drawings and exemplary embodiments.